A four or five-digit PIN is to be selected from the eight digits 0,1,2,3,4,5,6,7. 1. How many 4-digit PINs are possible if: a) all 4 digits are the same? e.g. 4-4-4-4 b) no digit can be repeated? c) any digit can be repeated? d) the first 2 digits must be different digits and the last 2 digits must be the same, but none of the first 2 digits can be used in the last 2? 2. Suppose any digit can be repeated, how many 4-digit PINs are possible if each PIN: a) must start with "1"? b) must not end with " 5 "? c) must neither start with "6" nor end with "6"? 3. Suppose no digit can be repeated, how many 5-digit PINs are Dossible if each PIN: a) must start with "1"? b) must not end with "5"? c) must neither start with "6" nor end with "6